Damping device for rotative wing aircraft



July 29, 1952 H. s. CAMPBELL 2,604,953

DAHPING DEVICE FOR ROTATIVE WING AIRCRAFT Filed Aug. 16, 1946 2 Sl-IEETS-Sl-IEET 1 AWE V702 HAQQIS SCAMPBELL ATT J y 1952 H. s. CAMPBELL 2,604,953

DAMPING DEVICE FOR ROTATIVE WING AIRCRAFT Filed Aug. 16, 1946 2 SHEETSSHEET 2 M11702 HAEQJS 36AM? ELL By g /k Afjami m d riment m t ons tot-t e i i cm -tf Patented July 29, 1952 ljAMPI'NG DEVICE FOREYROTKTIVEFWING ApplicationAugust16, 1946, Seri'al No; 6913;893'

1 l -This-invention relates to rotary-Wing airoraft and is more particularly directed toward damping -mechani'sm for the control of rotor blade movement. t I I In many types of rotary wing-aircraft a plu- -rality oi -blades are used, these blades being-attached to; a rotating part of the rotor hub by means, of 1-pivots. Horizontal or flapping pivots are used topermit motions by the individual i blades in-a directiongperpendicular to the? plane :OIarotation. Verticalor drag pivots are used in theattachment of the blades to allow 'thehlades :to move forwardly or rearwardly in the ,-pl a;ne -ofrota-tion from the radial position. Often-the blades are also mounted to permit-each b lade toychange pitch-for purposes oreontrol,

tWithwa rotor construction in which 'thGjIOljOl. iblades'a're ;c onnecte d toithe hub by means of drag :pivots; the; blades--'are.- free-to move to positions rin whieh they; are out oi ;pat-tern,- that is gthe snacmgrhetweem adjace t des mayrva rduringr operation. At; certain rspeedsof rotation; of therotor when: bladesalemounted in this {ash- :"1011' itis possible *to;dev,elop a critieal pr unstable condition ,Of operation-forexample when bringing the rotor unto-Speedxprior to flightg Spc h J critical 'frequenoiesrare "not necessarily the same 28 t "m at o a -$p d, F hQ"},Z.S iQP ZOP I- rides of thesupportingstructurepchiefly the land- -ing gear,- are also: involyed. :In;forder tggpreverit V the-development of-sach unstable motionsitfiis "necessary to; provide for damping-fin {*both {the :landin ar r tr ture; an Si the: r to -b d -m u When fi i tdamp n 1- ov d d atthese; points the blade1motions areprevented r0m;-- .s eck rwa sqalcqn nq s at 3 1 7 Claims; (01. He -#16625 5) V 'i a iie ievsqfi pe.qii ulierqt t q iiipr g nee anisin to eontro1 wthe instability dis- 5 ftli atlthe-hydraiilie gam jiii raice a u h r1- m lingi theiattacijnintfaf rt :a'nd he'elde'atidri-and mo'u degrees a ure 1 ent type .10

to which structure the arms I2 and |2a are rigidly" connected so that they movewith. the blade as it swings relative to the radial position. The

vertical pivot structure is adapted to be engaged by the blade fork T throughwhicha' horizontal pivot extends to permit flapping motions ofth'e:

blades.

In the present configuration the fork 1 is provided with a radially extending spindle on which bearings are provided for the support of sleeve 6. These bearings retain the blades against centrifugal force and permit pitch change movements to'be made; For the purpose of controlling these "pitch movements an arm 6a is connected to thej'blade terminal 6, the arm 6a being controlled by push rod' |-3 which connects by means -of arm 'Ma'to swash plate it; The swash plate may be moved'in a'fashion to provide for either simultaneous change of pitch for all the blades or cyclic change'of pitchfor controlpurposes. I

Connected between theend of the-arm l2 of one blade an'dthe arm l2a' of an adjacent blade a piston "type hydraulic unit generally indicated at |5i Attached to the housing [6' at one end'fare ears l'lto provide-'apivotal connection lfl fwith the end of arm: IZar- A piston 'rod' l9 -projects from the housing it and terminates in 'an adiustablefork end 20 to connect to arm l2 by meansofpivotzL The details of construction of thehydraulic 'unit I5 are cl early'i'llustrated 'in Figure-2; Here "'it'will be seen that the piston rod is extendsinto' the cylindrical bor e 22 inside the casing or housing 5. A piston member-231s provided at the when the rotor is operating at speed. When the rotor is stationary or operating at slow speeds the level of the fluid will be approximately horl zontal as indicated by the line 33h, since the main force acting upon it is the gravitational force. When the rotor is operating at high speed the centrifugal "forces acting'on the hydraulic fluid in reservoir 33 predominate 'so' that the fluid tends to move to the outboard side of the reser- "voir' with the result that the fluid level may be almost vertical as indicated by the line 330 in the hydraulic valves.

- tive position.

Figure 3. Under either condition the inclined position of the reservoir assures that the fluid willcover the outlets. A lid 34 which may have a vent 3t'a'jis provided for filling reservoir 33.

At the ends of channels or bores 3| and 32 there are plugs .35 provided to permit access to the bores for assembling the various parts of In each of the bores 3| and 32 there is provided a valve part 36 with a shank portion adapted to support the valve in the bore Each valve 36 is providedwith an encontact the seat 38 at the inner end of bores 3| and 32, respectively. A spring 39 is proportioned to fit between valves 36, 36, to 'urge them into contact on their respective seats. E'ach valvepart is provided with a central channel 4ll, o'nefend of which is beveled to form a seat suitable for contact'with the tapered end ofp'oppet part 4|. -An orifice 42 is located in the end of'poppet {it and connects with bore 4|] in the ,'valve 36.

v A light springdfi reacts between the plug 35 and'the poppet 6| to retain it inopera- It will be seen that an external channel is provided at certain pointson thecircumference "of poppets 4| and valves 36. This is illustrated .end of rod |9 with'a groove having suitable (iirnensions for'retaining a; sealing ring 24. The

"piston 23jis provided "with shoulders 25 and 25a of reduced diameter. These shoulders are pro- "portioned' to contact theends of the cylinder 7 while still allowing free accessof the fluid in the cylinder to the holes 26 and 2} at each end of the jcylinderu rtwi'n be'observed'that one end r thecylinder is closed by means of threaded plug z s having a suitable aperture tof'allowsliding movements of the piston rod l9; A hydraulic seali"29"is imounted in the'plug 28"and"'ja wiping" or oiling ring 30 is provided to prevent entranceofdirt which might interfere withffree' slidingfof the rod. An oil hole3ta is provided to allowperio'dic oiling of the seal 30 which may be or felt or other suitable material; It will be noted that the plug 28 is of relatively great length in order to provide a considerable bearing area in contact l6 and'as wmbe observed in Figures 1 and 3, lies at an angle of approximately 45 degrees in Figure 2 by the space at the lower sideof the valves 36 and poppets 4l-where they are clear of the surface of bores 3| and 32. Suchachan- "nel'may be provided by-machining'suitablesflat surfaces on the cylindrical portions of the valves 36' and poppets 4|; .This 'will be more readily seen in Figure 3' wherethe' three flat surfaces-on The" operation of the damping dBVICBS" illustrated: in Figures 1- to 3 is as follows.- When the *piston is moved to the right, pressure is built -up-inthe right hand end of the cylinder and creased speed due to the restriction to flow offered by orifice.- Upor'r exceeding a given pressure; which pressure --is I determined by.- the capacity of spring arena 1 the. area of channel 3 l the *valvepart 3'6fisfcau'sed"tof inove against the force o'fspring 39; This movement causes valve 3B=to lift from theseat 38'and'thus'permits additional free flow around the outside 'of' poppet 4| and valve 36 therebyylimitingfihe' pressure de- -veloped by the piston-to a predetermined value.

4, 1 v. n i therie reduced "pressure is, produced" n the-cylinder to the t of Qn';2 'I rde to e thi pa oithe cylinder'full of fluid, flow .occur s'from the During the motion oflt reservoir 3-3"-thro'ughthe channels'32 and 21 into unrestricted since'thecapacity of light spring 4 3 with respect to the' vertical when in position on the rotor; This relative positioriingof the reser-'- voir provides for covering the bottom outlets from the reservoir'to channels 3| and 32 with,

hydraulic fluidwhen the rotOr is-statiOnary or the am cylinder-Q This now is comparatively is extremely low-'andas gsoon as 'a lower pressure I develops in channel 32: 'than'in thereservoir 33, flew. occurs withouti appreciable restriction through the channel 40 of valve 36, past the seat adaptedto be double. on the damper .unit will build up-a pressure in the through channel ,tion ,of the piston; to the rightsubstantially ,un-

. movement of the motions in the damper mechanism. As has prethe blade about pivoti may occur.

,,tached,- This arrangement 1 for blade to hub dampingas arrangement shown in l igure a' fashion to allow free blade movements in fl ppin s na c, 1:; 1 -From; the foregoing description, it, will b e'evident that I have provided a-simple form of hy- .draulicgdamping device which -is particularly pets: and" pressure yrele channel; .1 l orll I a causing. one of the ,poppets 8| to open and permit flowfrom thecorresponding cylinder ,chamberJ; If. desired an orifice mayhe provided through the poppets Si .130 allowarestricted flow at pressures below the opening-presw sure. Thisis illustrated in Fig. ,6, wherein poppet valve,8 l a, corresponding generally ,to valve 8 I of .Fig.fl5,', has v a restricted axial .orifice 8L1)v in its seatinglend. 1

With this construction, thejdamping device is acting. A ,compressionsload right hand end of the chamberandl n reaching sufiicient magnitude-l the compression load will cause movement, since the, poppet- 8! will open at the ;.predetermined. pressure, and allow-gflow H to the reservoir. During morestricted flow from the reservoir to; the left hand .end of the cylinderris permitted through channels 14 and I2 andthen through the left hand check valve it to channel Ha. Atension load on the damper unit will cause motion of the piston to the left and thus cause operation of the poppets and check valves in the opposite sense to that just described. f I p 7 U Duringfiight operation each rotor blade may move from radial position55r to a forward position represented by centerline 55 and a lag position represented by centerline 551). This blade causes v directly related viously, been discussed, duringstarting or stopping operations on the groundthe rotor passes I through .critical speeds and similarmotions of These motions are damped by meansof the energy absorbed by thedamping devicefi and are thus prevented from developing to an undesirableamplitude. The dampers illustrated in Figure 4 blade .to which arm '51 is attached and the hub to whichtheinner end of the damper is at- 1 where blade to blade, damping is illustrated The configuration of the hub and blade connection in Fig ure l is such that the flapping pivot is offset from a the drag pivot, the latterbeing considerably outboard thejflapping pivot.

The mounting of the damper is arrangedto dampen only the drag pivot movements, the damper being supported in effective for use-with pivotally mounted blades on rotative wing aircraft. The arrangement of valves and poppets to provide a compact and light weight unit having safety featuresv to prevent the development of excessive bending moments in blade structures provides :;a .unit having inv creased value for this damping-function. The

; particular arrangementof or fice within the popfzz e ani m s 1 al particular advantage in providing" compactness and low weightgwhileatithesame time allowing for simple assembly.

-rIclaimzv a 1.- Adamping device for an aircraft rotor-having a cylinder, a piston member, a fluid reservoir,

. channel leading from said; cylinder to. said of dampers provides compared to. the v the I reservoir, a check valve in said channel allowing free flow of fluid from said reservoir.tosaid'cyl- .inder when the pressure in saidcylinder is lower than, the pressure in saidreservoir, an orificein said check valve to allow restricted new from said cylinder to said reservoir under cylinder pres'snre, .a movable seat member against whichsaid check .valve seats, and, spring means retaining said seat 'member against a fixed seat thereby providing .for limiting the pressurein said cylinder to a predetermined value. p

2- A am i g de c voir, a channel e in lfrpm sai l n r to id control: each of the blades .individually, since 7 ithepdamping restrai t isapplied between; the

'r se v ina e ody avi al s rin contacting it to provide a check valve which opens to allow flow from said reservoirto said cylinder when the pressure in the cylinder is lower than in the reservoir, and a second valve body; having a heavy spring-contacting it to; provide a pressure relief valve which opens. to allow flow from said cylinder to said reservoir at a predetermined pressure one of said valve bodies being provided with a female seat against-which the other of said valve bodies makes (:Qntact, and a restrictive orifice in one of said valve bodies, 3. A damping devicefor an aircraft rotor havinga cylinder, a piston member, a fluid reser- -voir, achannel leading from said cylinder to said reservoir, a valve body having a light spring contacting it to provide a check valve which opens to allow flow from saidreservoir to said cylinder when the pressure the cylinder is lower than in the reservoir and a second valve body having a heavy spring contacting itto prpvide a pressure relief valve whichopens to allowflow from said cylinder to said reservoirat a predetermined pressure, one of said valve bodies be- ;ing provided withafemale seat againstwhich and a: restrictive; orifice in the valve, bodywhich contactssaidfemaleseat r the other of said valve bodies makes contact,

, 4,. A damping device for: an aircraft rotor shaving a cylinder, a piston me mber, a fluidresert,voir, a channel leading from said cylinder tQsald reservoir, a valve body having'alightspring contacting it to provide a check valve which opens to -allowfiow from saidreservoirto saidcylinder ,{when :thepressure in the cylinderis lower than in the reservoir, and a second valve body having aheavy spring contacting lit-to provide a pres- .;sure relief valve which opens to allow-flow from 'said'cylinder to said-reservoirat a predetermined "jpressure, oneof saidyalve bodies being provided 1 witha female seatfagainst which theother of said valve ibodies makes contact. c.

5. In. combination; an aircraft rotor having blades pivoted for limited motion aboutan aXis parallel'to the main rotor axis, and-a damping V saidte1escopirigparts extending rotation ofvsaid rotorl 7 device therefor comprising fluid-containing, telescoping parts, one of which is attached to a blade of the rotor and the other of which is attached to another part of the rotor structure so thatthe linejof reciprocationof the'sai'd telescoping parts 1 subs ant l pera i th ee 6f t 'ei .rin"theou rof imw dm. 'fro'niwith its free end inclinedtoiwardlthea /6. j An aircraft rotor having for lead-lag movement about a substantiallyjvertical L ax s, a hydraulic damping device having telescoping parts including a cylinder and a piston, L mpiinting' means attached to said cylinder hav-- 1 .1%? s bsfanea ri i P P EP$ q m for an aircraft rotor hav .ing atylinder apiston member, afluid resera fluid reservoir attached to said cylinder and having its axis inclined upwardly and inwardly when said cylinder is supported inoperative position on said member.

7. A hydraulic damping unit for an aircraft rotor including a body member having a cylindrical bore chamber, a pistonmounted in said chamber for double acting damping motions therein, said body member having two fluid channels each having its axis parallel to the axis of said chamber, a fluid reservoir associated with said body member at approximately the longitudinal center thereof, a fluid connection between said reservoir and the middle of each parallel channel, a fluid connection from each channel to each end of said chamber, valve means in each channel between the reservoir connection and the chamber connection, the valve means in one channel being adapted to allow substantially unrestricted flow from said reservoir to said chamber, said valve means including an imperforate body, and the valve means in the other 10 1 channel also having an imperforate body adapted to provide flow from said chamber to said reservoir only upon development of a predetermined pressure in said chamber.

HARRIS S. CAMPBELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 456,016 Canet July 14, 1891 1,291,016 Kellogg Jan. 14, 1919 1,614,657 Cotton Jan. 18, 1927 1,836,381 McNab Dec. 15, 1931 1,899,096 Larsen Feb. 28, 1933 1,948,457 Larsen Feb. 20, 1934 2,003,010 Nixon May 28, 1935 2,046,889 Wyeth et al. July 7, 1936 2,239,112 Nickelsen Apr. 22, 1941 2,318,260 Sikorsky May 4, 1943 2,554,774 Buivid May29, 1951 

